I use sdkman to install each and every Gradle release or RC in several different environments (all Mac or Linux). I have not had any issues with any release so far.
Since your post, I’ve uninstalled, flushed, and installed Gradle 2.14.1, Gradle 2.14, Gradle 3.0-milestone-2, and a couple other random versions. I have not experienced any cases where sdkman doesn’t succeed in the install.
I have also done the same without any problems. I have already commented on the same Github issue mentioned above.
My only guess would be that we had a faulty proxy handling redirects after being initially redirected from SDKMAN (which explains why vertx was fine). Also worth mentioning that we have had no further complaints regarding this.